In fabricating semiconductor devices, steps of processes are performed on a wafer of a semiconductor substrate by use of a number of semiconductor manufacturing apparatuses. Such processes include, for example, the thin film formation on the wafer, etching process of the wafer or the thin film on the wafer, implantation of impurities, thermal treatment, exposure and development, and the like. Through the use of semiconductor manufacturing apparatuses in wafer processes, the wafer is processed with multiple processing parameters such as processing conditions. Such a processed wafer needs to have target parameters, which are physically, optically, or electrically measured from the processed wafer, within desired ranges. The yield of the semiconductor devices can be maintained by keeping the target parameters of the wafer within the desired ranges, thereby enabling the production costs to be reduced.
Japanese Patent Application Publication No. 6-4789 discloses an error monitoring method in which characteristics of the apparatus to be monitored or neighboring equipment thereof are detected, multiple regression analysis is performed on the characteristics, and the regression coefficient is judged as to whether it lies within a given normal range. If the regression coefficient does not lie within the given normal range, it is determined that an error has occurred in the apparatus.
As a method of making the target parameters lie within a desired range, one or more of the processing parameters of the semiconductor manufacturing apparatus are modified prior to the wafer processing, based on the target parameters measured from another wafer. The processing parameters, however, have variations in a short range. Even with the afore-described method, the desired target parameters are not always obtainable. While one process is being performed, there are, for example, ten to hundred processing parameters of the semiconductor manufacturing apparatus. For this reason, keeping the target parameter within a desired range proves difficult.